690 Mr. E. Marsden and Dr. P. B. Perkins on the 



more rapidly than corresponds to the true absorption of the 

 crystal. 



(iii.) Comparison with experiment suggests that the new 

 formulae can account for the observed intensity as little as 

 the old. 



(iv.) This observed strength of reflexion is to be attributed 

 to crystalline imperfection, and allowing for this the old 

 formulae of the first part are retained with a new numerical 

 factor. 



My thanks are due to Prof. Sir Ernest "Rutherford for the 

 kind interest he has taken in this research. 



March 4, 1914. 



LXXIX. The Transformations in the Active Deposit of 

 Actinium. By E. Marsden, M.Sc, Lecturer in Physics, 

 and P. B. Perkins, Ph.D., University of Manchester*. 



IT is well known that the " C " products of the active 

 deposits of radium and thorium are anomalous in that 

 in both cases the atom has two distinct modes of trans- 

 formation, i. e. it breaks up with emission of either an u or 

 a /3 particle. In the case of thorium C, owing to the fact that 

 the chance of disintegration in either of the two ways is of 

 the same order, it has been found possible to examine the 

 process in considerable detail, and the following scheme of 

 transformation has been arrived atf: — 



a (5.0) a (5.7) Py a (4.^Th^-^? 



ThEm- *Thl ► Tl/B^ > Th C ^ 3 '° 7 minS ' 



\, \^ f- (8.6) 

 54 sees. ,0.14 sec. 10.6 hrs. (B >* Th'Q, — *? 



60.5 mins. 10" spcs. 



By analogy the method of production of the branch product, 

 2 , has been deduced %. 



* Communicated by Sir E, Rutherford, F.R.S. 



t Marsden & Barratt, Proc. Phys. Soc. xxiv. 1, p. 50 (1911) j Marsden 

 & Darwin, Proc. Roy. Soc. A. lxxxvii. p. 17 (1912) : Marsden & Wilson, 

 P hil. Mag. xxvi. p. 354 (1913). 



X K. Fajans, Phys. Zeit. xii. p. 369 (1911) ; xiii. p. 699 (1912). 



